An image display unit, which displays an image by irradiating an electron beam which is emitted from an electron source to a phosphor material to cause the phosphor material to emit light, generally has the electron source and the phosphor material within a vacuum envelope. When gas (surface adsorption gas) adsorbed to the inner surface of the vacuum envelope is separated to lower a degree of vacuum in the envelope, electrons emitted from the electron source are disturbed from reaching the phosphor material, and a high-brightness image display cannot be made. Therefore, it is necessary to keep the inside of the vacuum envelope under high vacuum.
The gas generated in the envelope is ionized by the electron beam and accelerated by an electric field to collide the electron source, possibly damaging the electron source.
The conventional color cathode-ray tube (CRT) or the like retains a desired degree of vacuum by activating a getter material disposed in the vacuum envelope after sealing and adsorbing the gas released from the inner wall to the getter material during operation. And, it is now being attempted to apply the achievement of a high degree of vacuum and the retention of a degree of vacuum by the getter material to a flat type image display unit.
The flat type image display unit is provided with an electron source which has multiple electron emitting elements arranged on a flat substrate. The capacity of the vacuum envelope is considerably reduced as compared with that of an ordinary CRT, but the surface area of the wall releasing the gas does not be reduced. Therefore, when the surface adsorption gas in a volume similar to that of the CRT is released, deterioration of the degree of vacuum in the vacuum envelope becomes quite substantial. Accordingly, the getter material plays a very important role for the flat type image display unit.
Recently, formation of a layer of the getter material in an image display area is being studied. For example, Japanese Patent Laid-Open Application No. Hei 9-82245 discloses a flat type image display unit having a structure in which a thin film of a getter material having conductivity, such as titanium (Ti), zirconium (Zr) or the like, is overlaid on a metal layer (metal back layer) which is formed on a phosphor layer or the metal back layer itself is comprised of the getter material having the conductivity.
The metal back layer is aimed to enhance brightness by reflecting to the face plate side the light advancing toward the electron source in light emitted from the phosphor material by the electrons emitted from the electron source, to play a role as an anode electrode by imparting conductivity to the phosphor layer, and to prevent the phosphor layer from being damaged by ions generated by ionization of the gas remained in the vacuum envelope.
The conventional field emission display (FED) had a disadvantage that an electric discharge (vacuum arc discharge) was easily caused when images were formed for a long period because a face plate having a phosphor screen and a rear plate having an electron emitting element had a very small gap (space) of one to several millimeters between them, and a high voltage of about 10 kV was applied to the small gap to form a high electric field. And, when such an abnormal electric discharge occurred, a large discharge current in a range of several amperes to several hundred amperes flowed instantaneously, so that there was a possibility that the electron emitting element of a cathode section and the phosphor screen of an anode section were destructed or damaged.
Lately, it is proposed to form a gap section in the metal back layer being used as the anode electrode in order to ease the damage resulting from the occurrence of an abnormal electric discharge. An image display unit configured to have the metal back layer coated with a getter layer having conductivity is proposed to have a gap in the getter layer by forming the getter layer in a specified pattern in order to additionally restrict the occurrence of electric discharge so as to improve a withstand pressure characteristic.
Conventionally, as a method of forming the getter layer having a specified pattern, there is proposed a method of disposing a mask having a pore pattern on a metal back layer and forming the getter layer by a vacuum-deposition method or a sputtering method. But, this method has disadvantages that patterning accuracy, pattern fineness and the like are limited, and an advantageous effect of preventing an electric discharge to improve the withstand pressure characteristic is not sufficient.
The present invention has been made to remedy the above disadvantages and provides an image display unit capable of providing a high-brightness, high-grade display with electron emitting elements and a phosphor screen prevented from being destructed or deteriorated by electric discharge, and a manufacturing method thereof.